Spectroscopic lamp



Oct. 18, 1955 N, Q BEESE 2,721,285

SPECTROSCOPIC LAMP Filed May 27, 195:5

INVENTOR N. CvBE'-SE'.

ATTORNEY SPECTRQSCOHC LAMP Norman C. Beese, Verona, N. J., assigner to Westinghouse Electric Cor-poration, East Pittsburgh, Pa., a corporation of Pennsylvania' vAprlisatifm May 27, 195s., Serial No. 257,614

9 claims. (61.313-25) This invention relates to arc lamps and, more particularly, t spectroscopic helium arc lamps- HeretOfQre it has been .known that helium are lamps are very useful as a spectrosopic light source, for such lamps produce very sharp spectral lines at 1.08 mu and 2.0.6 H111 in the infrared, 3,889 A U. in the ultraviolet, and several frequencies in the visible spectrum. A spectral distribution for helium may be found in Handbook of Chemistry and Physics, 33rd edition, p. 2303, published by the Chemical Rubber Publishing Company, Cleveland, Ohio (1951).

In most lamps, spectroscopic lamps included, it is,.,of course, desirable to maintain the highest operating efciency possible, and to have an output which is relatively constant throughout the life of the lamp. In addition, the life of the lamp should be as long as possible.

Helium spectrosopic lamps preferably operate at relatively high temperatures and wattages, a representative average temperature being 3139 ,.C., a representative maximum temperature being slightly above 50.0 AC., and a representative wattage being 225 watts. Because of these relatively high temperatures, the vitreous envelope containing the helium arc is preferably fabricated of fused quartz, which will withstand the high operating temperatures. At these high operating temperatures, however, the fused quartz envelope is quite porous to the light gases, i. e., helium and hydrogen, resulting in a decrease of the helium charge within the quartz envelope. This leakage of the operating charge of helium gas modiies the operating characteristics of the spectroscopic lamp, which lamp, of course, desirably has operating characteristics which are quite stable. Further, it is impossible to maintain the light gas operating pressures which will resultin a suitably stable operational eiciency, not only because of the loss of operating gas through the envelope, but because of the cleaning-up of the operating gas vduring operation of the lamp.

,It is the general object of the invention to avoid and overcome the foregoing and other difficulties of and objections to prior art practices by the provision of a vitreous outer envelope surrounding the inner fused quartz envelope, and by providing a sealing charge of light gas within the volume enclosed between the two envelopes.

A further object of my invention is to provide a vitreous outer envelope to surround the inner fused quartz envelope and to include between the inner and outer envelopes a reservoir o f light gas in order to make up any operating light gases within the inner envelope which may be cleaned up during operation.

It is another object of my invention to provide a vitreous outer envelope to surround the inner fused quartz envelope and to include between the inner and outer envelopes a sealing-reservoir charge of helium gas of such pressure that Vthe average operating pressure of the helium gas within the fused quartz envelope and the average pressure during operation of the helium reservoir and sealing gas between the two envelopes are approxi,-

rnately the same.

Patented Oct. 18, 1955 Yet another object of my invention is to provide an inert gas within the volume bounded by the inner surface of the outer envelope and the outer surface of vthe inner envelope, in order to facilitate starting.

A still further object of my invention is to provide a discharge lamp with inner and outer envelopes, which lamp has a hydrogen gas reservoir and sealing charge be.- tween the two envelopes, and utilizes an Voperating `charge of hydrogen gas within the inner envelope. Y

AAnother object of my invention is to provideallowable and optimum limits for the ,operating pressures of .the sealing-reservoir charge and operating charge in my lamp, at which pressures the spectral radiation from 4the arc discharge will be maintained within the corresponding allowable limits or at an optimum.

The aforesaid objects of the invention and other objects which will become apparent as the description proceeds are achieved by providing a light gas spectroscopic lamp with inner and outer envelopes wherein the light gas discharge occurs within the inner envelope and the volume between the inner and outer envelopes contains a sealingreservoir charge of light gas, which sealing-reservoir charge has a pressure, during operation of the lamp, approximately equal to the pressure during lamp operation of the operating charge of light gas contained within the inner envelope. In addition, the operating charge may be maintained within allowable limits or at an optimum, which will result in an increased intensity of spectral lines produced.

For a better understanding of my invention, reference should be had to the drawings, wherein:

Fig. l is a sectional View of the preferred embodiment of my invention illustrating the double vitreous envelopes, electrodes, lead-in conductors, and necessary electrical connections for my lamp;

Fig. 2 is a graph of the relative gas pressures within the inner envelope and within the volume between the inner and outer envelopes as ordinate vs. static conditions, Warming up period, and steady-state operating conditions as the abscissa. The sealing-reservoir gas pressures be'- tween the inner and outer envelopes are represented as a dotted line and the operating gas pressures within the inner envelope are represented as a solid line;

Fig. 3 is a graph representing the ultraviolet radiation relative intensity/ volt-ampere of the helium arc discharge as ordinate vs. helium operating charge gas pressure in mm. mercury as abscissa. This ultraviolet radiation is largely 3889 A. U.; i

Fig. 4 is a graph representing visible light relative intensity/volt-ampere of the hydrogen arc discharge as ordinate vs. the hydrogen operating charge gas pressure in mm. mercury as abscissa. I

Although the principles of the invention are broadly applicable to any discharge lamp wherein the operating gas pressures are to be maintained within allowable limits within an envelope which may be porous with respect to said operating gas, the invention is usually employed in conjunction with a spectroscopic helium arc lamp and hence it has been so illustrated and will be so described.

With specific reference to the form of the invention illustrated in the drawing, the numeral 10 indicates the spectroscopic lamp, generally, which lamp comprises an outer envelope 12, inner envelope 14, electrodes 16 and k18, a plurality of lead-in conductors 20, reentrant press 22, base 24, and electrical contact pins 26. The inner envelope 14 consists generally of a hollow tubular fuzed quartz portion 28, graded seals 30 fuzed to the end of quartz portion 28, and a high coefficient of thermal expansion sealing glass 32 fuzed to the ends of graded seals 30, through which the plurality of lead-in conductors 20 are sealed. As heretofore noted, the hollow tubular portion 28 of inner envelope 14 is preferably of fuzed quartz in order to withstand the relatively high operating temperatures which may be 300 to 550 C. Quartz cannot be sealed, however, to the tungsten lead-in conductors because of the differences in coefficients of thermal expansion of the quartz and the lead-in conductors'. Accordingly, graded seals 30 are provided at either end of the tubular quartz portion 28, in order to bridge the difference in the coefficients of thermal expansion of quartz and that of the high coeicient of thermal expansion glass seals 32 which are fuzed to the ends of the graded seals 30 and which will form satisfactory hermetic seals with the plurality of lead-in conductors 20. This practice is very common in the art. The glass seals 32 may be fabricated of any glasswhich softens'at temperatures above 500 C. and has a suitably high coefficient of thermal expansion.

While the glass seal 32 Will satisfactorily seal to the lead-in conductors 20, it is preferable to first bead the leadin conductors 20 with a glass bead 33 before fuzing the seal 32 around lead-in conductors 20. lt has been found that a glass manufactured by the Corning Glass Works and designated as Corning Code No. 724, which is a sodium-potassium-borosilicate glass, may be satisfactorily beaded onto the lead-in conductors 20. Between this glass bead 33 and the graded seal 30 it has been found that a glass manufactured by the Corning Glass Works and designated as Corning Code No. 723, which is borosilicatealumino glass, will be satisfactory as the glass seal 32. The graded seals are very common and Well-known in the art, and consist of a series of glasses running in succession from a low coeiiicient of thermal expansion at the quartz connecting ends to a relatively high coefficient of thermal expansion at the other ends, in order to bridge the difference in coefficients of thermal expansion between the quartz 28 and the sealing glass 32, as heretofore noted.

The plurality of lead-in conductors 20 may be fabricated of a refractory metal such as tungsten or molybdenum and are hermetically sealed through the inner envelope 14 and outer envelope 12. The plurality of lead-in conductors 20 are hermetically sealed through the outer envelope 12 by means of a reentrant press 22, as is common in the art. The plurality of lead-in conductors 20 may terminate at the exterior of the outer envelope in electrical contact adapters, such as contact pins 26 contained in a base 24 at one end of the outer envelope 12, as illustrated, or the plurality of lead-in conductors 20 may be sealed through both ends of the outer envelope 12 as is common in the fluorescent lamp art.

The electrodes 16 and 18 are supported by lead-in conductors 20 and are substantially similar to the electrodes disclosed in my Patent No. 2,562,887, dated Aug. 7, 1951, and assigned to the present assignee. The electrodes 16 and 18 are identical and are positioned approximately at opposite ends of the inner envelope 14. Each electrode 16 and 18 consists of a cathode 34 comprising an oxide coated refractory metal such as tungsten or molybdenum terminating in an electrode tip 35, and a torroidal anode 36 fabricated of a refractory metal such as tungsten or molybdenum.

The outer envelope 12 may consist of any suitable hard glass which softens at temperatures above 500 C. and is impervious to light gases. Pyrex may be used as an outer envelope, if desired. Pyrex is a Corning Glass Works trademark for a borosilicate-alumino-sodium-potassium glass. The outer envelope 12 may take any desired shape, but is preferably of a generally hollow cylindrical shape, with one end closed and the other end sealed by a reentrant press 22, as illustrated. The press 22 also includes a tipped-off exhaust tube 37, as is common in the lamp art.

Contained within the inner envelope 14 is an operating charge 38 of helium gas which is preferably of the highest purity obtainable which charge is introduced through tipped-off exhaust tube 39. Contained between the outer envelope 12 and the inner envelope 14 in what may be referred to as a sealing-reservoir volume is a sealing-reservoir charge 40 of helium gas at such pressure that during operation of the lamp the pressures of the operating charge 38 of helium gas within the inner envelope 14 and the sealing-reservoir charge 40 will be approximately equal. It has been found by experimentation that if the foregoing gas-pressures of the operating charge 38 and the sealing-reservoir charge 40 are to be equal during Operation of the lamp, in the embodiment illustrated and described, the static or non-operating pressure of the helium operating charge 38 will be slightly more than half the static or non-operating pressure of the helium sealing reservoir charge 40. Knowing the operating temperatures and the gas constants forthe gases involved, the pressures which will be encountered during operation may be readily calculated by Boyles and Charles Laws, see Handbook of Engineering Fundamentals, second edition, Eshbach, page 8-15, John Wiley and Sons, Inc., New York (1952).

In Fig. 2 are representative curves illustrating the pressures of the sealing-reservoir charge 40, shown as a dotted line, and the operating charge 38 shown as a solid line, of helium gas within the envelopes 12 and 14, during nonoperating or static conditions, during the warming-up period, and during steady-state operation. As illustrated, and as heretofore noted, during the static or non-operating condition the pressure of the sealing-reservoir charge 40 of helium gas in the embodiment as illustrated and described will be slightly less than twice that of the nonoperating or static gas pressure of the operating charge 38.

Also contained within the volume between the outer envelope 12 and inner envelope 14 is a starting charge 42 of argon and/ or nitrogen gas. It has been found convenient to maintain a static or non-operating total gas pressure between the envelopes 12 and 14 of one atmosphere, and accordingly, if the partial pressure of the helium gas sealing-reservoir charge 40 is to be 4 mm. mercury, the partial pressure 0f the starting charge 42 will be approximately 718 mm. mercury. The purpose of this starting charge 42 is purely to facilitate starting, for without it, the low pressure of the helium gas sealing-reservoir charge 40 would tend to cause an arcing over the lead wires adjacent the glass reentrant press 22, rather than permitting the establishment of an arc within the inner envelope 14.

In Fig. 3 is shown a graph of the relative intensity/ voltampere of the 3889 A. U. helium spectral line vs. the pressure of the helium operating gas 38 under operating conditions. These intensities were measured with an ultraviolet sensitive photocell, and as plotted represent only relative values for purposes of comparison. As may be seen, the curve is somewhat exponential in nature, having a low relative intensity of 1.8 at 12 mm. mercury pressure of operating gas 38 and a peak relative intensity of 16 at approximately 0.5 mm. mercury pressure of operating gas 38. As may be seen, the curve starts to break at a relative intensity of 3.8 at about 6 mm. mercury pressure of operating gas 38. It has been found through experimentation that it is desirable to maintain the operating pressures of the operating gas between about 0.5 mm. mercury and 6 mm. mercury in order to maintain operation of the lamp at the more efficient operating pressures.

Light gas discharge lamps tend to clean up or decrease the operating charge 38 during operation, and the pressure of the operating charge 38 will thus gradually decrease during operation both through dispersion of the operating charge 38 through the fuzed quartz envelope, and through the heretofore noted cleaning up of the operating charge 38. It might be possible in some cases to make the inner envelope 14 sufficiently large to enclose a suitable reservoir of light gas in order to maintain the operating charge 38 within allowable limits for a suicient period of time to give the lamp a reasonable life. Such a larger inner envelope, however, is impractical where a positive column discharge is to be maintained, since such a discharge requires a relatively narrow cross-sectional configuration in order to satisfactorily form this type of discharge; space limitations are also a consideration. It is for this reason that the outer envelope 12, which is impervious to light gases, is required, in order to contain a reservoir of light gases to make up that portion of the operating charge 38 which is cleaned up within the inner envelope 14, and to seal the operating charge 38 within the inner envelope 14.

As may be seen from Fig. 3, if it is desired to operate my lamp at a maximum eiiiciency, the pressure of operating charge 38 during steady-state operating conditions should be maintained between 0 5 and l mm. mercury.

For one speciic embodiment of my invention, the following lamp dimensions and gas-till pressures are given:

Overall length of cylindrical outer en- 11" velope. Average diameter of outer envelope 2 Overall length of cylindrical inner en- 6" velope. Average diameter of inner envelope 3A" Distance between electrode tips 3" Operating helium gas pressure within inner 025-3 envelope (non-operating conditions- 20 C.). Partial pressure of sealing and reservoir 0.47-55 mm.

charge of helium gas between inner and outer envelope (non-operating-ZOo C.). Partial gas pressure of starting charge of approx. 70 cm.

argon and/ or neon (non-operating condition-20 C.). Operating voltage 150 volts Operating current 11/2 amps.

Operation When the energizing potential is applied across the lead-in conductors 20, a portion of the operating charge 38 'between4 electrodes 16 and 18 will ionize and an are will strike between the electrodes. When the arc is first struck, the entire lamp is normally at a room temperature of about 210 C., at which temperature the quartz portion 2,8 of inner envelope 14 is impervious to light gases. As soon as the arc is struck, however, the temperature within the inner envelope 14 will rise sharply, stabilizing at an average steady-state temperature around 310? C. At this average steady-state operating temperature the quartz portion 28 of inner envelope 14 will be at a temperature of about 500 C. and at such a temperature is quite porous to light gases. The sealing-reservoir charge 40 and starting gas charge between the inner 14 and outer 12 envelopes will also heat during operation, but to a muoh lesser degree because of the increased volume and surface area of the outer envelope 12. When the steady-state operating conditions have been reached, the pressure of the operating charge 38 of helium gas within the inner envelope 14 and the partial pressure of the sealing-reservoir charge 40 between inner 14 and outer 12 envelopes will be substantially equal. Of course, when steady-state operating temperatures and conditions have been reached, the helium gas will diffuse through the quartz portion 23 of inner envelope 14 with considerable rapidity, but there will be no net flow of helium gas into or out of the inner envelope V14 because of the equal pressures of helium on both sides of the tubular quartz 28.

During operation of the lamp, a portion of the operating charge 38 will be cleaned up as heretofore noted, and the operating charge 38 pressure reduced accordingly. The sealing-reservoir charge 40 will make up this loss, since the partial pressures of the light gas on either side of the quartz portion 28 of inner envelope 14 will be substantially the same during operation. Of course the cleaning up will have the effect of decreasing the sealing-reservoir charge 40, but because of the greater Volume of sealing-reservoir charge 40 enclosed between the outer envelope and inner envelope, this gradual vdecrease in the pressure of the operating gas charge 38 throughlclea.ning up does not measurably decrease the life of the lamp or change the operating characteristics. It is obvious that the volume contained between the inner envelope 14 and outer envelope 12 is not limited by design considerations, and, accordingly, within reasonable limits the outer envelope 12 may be enlarged. Thus the operating characteristics of the lamp are not appreciably aif'ectedY by any change in the helium operating charge38. `It should be noted that the quartz portion 28 of( innernenvelope 14 is impervious to the starting charge of the heavier argon Aandi/or nitrogen gas contained between the inner envelope 14 and outer envelope 12, even at operating temperatures above 500 C. and these heavier gases in noV way atect the operation of the lamp, except as concerns starting, as hereinbefore noted.

It will be recognized that the objects of the invention have been achieved by providing a light gas spectroscopic lamp which has a long life, can be operated at constant efficiency, and if desired, the operating eiciency can be maintained at an optimum for long periods of time.

As a possible alternative structure of the preferred embodiment of my spectroscopic lamp, the operating charge 38 and sealing-reservoir charge 40 may be hydro'- gen. In Fig.` 4 is shown a graph of the relative intensity/volt-ampere of the visible spectrum v s. the pressure of the hydrogen operating gas 38 under operating conditions. These intensities were measured with a visible light sensitive photocell, and as plotted represent only relative values for purposes of comparison. As can be seen, the curve is somewhat exponential in nature, having a low relative'intensity of y1.4 at 7'mm. operating gas pressure and a peak at a relative intensity of 10 at approximately 0.6 mm. mercury operating gas pressure. As may be seen, the curve starts to break at a relative in- .tensity of 1.6 at about 4 mm. operating Vgas pressure. It has been found through experimentation that it is de- Sirable to maintain the operating gas pressures between 0.6, and 4 mm. in order to operate the lamp at a more ecient operating pressure. If it is desired to operate at a maximum of eiiciency, the operational pressure of the operating charge 38 may be maintained between 0.6 and 0.8 mm. mercury.

While in accordance with the patent statutes one best knownembodiment of my invention has been illustrated and described in detail, it is to be particularly under- .Stood that the invention is not limited thereto or thereby.

I claim:

1. A light gas discharge lamp comprising a vitreous sealed outer envelope surrounding a fuzed quartz sealed double-ended inner envelope, said envelopes having inner and outer surfaces and lead-in conductors sealed therethrough, electrodes positioned within said inner envelope and substantially at opposite ends'thereof and supported thereat by said lead-in conductors, an operating charge of light gas contained within said inner envelope, said lead-in conductors and said electrodes being adapted to have applied thereto an energizing potential for ionizing and converting a portion of said operating charge into a steady-state light gas are discharge between said electrodesfsaid operating harge having an average steadystate operating pressure during -saidsteady-state light gas are discharge, a sealing-reservoir volume bounded 'by said outer euvlQP@ inner Surface and said inner envelope outer surface, alight gas sealing-reservoir charge contained within said sealing-reservoir volume and of such magnitude that its average pressure :during said steadystate light gas are discharge approximates said average steady-state operating pressure of said operatingcharge, and a starting .charge contained within said sealing-reservoir volume for maintaining said light gas arc discharge within said inner envelope.

2. Aspect'roscopic lamp comprising a vitreous sealed outer envelope surrounding a fuzed quartz sealed doubleended inner envelope, vsaid envelopes having inner and outer surfaces and lead-in conductors sealed therethrough, electrodes positioned within said inner envelope and substantially at opposite ends thereof and supported thereat by said lead-in conductors, an operating charge of helium gas contained within said inner envelope, said lead-in conductors and said electrodes being adapted to have applied thereto an energizing potential for ionizing and converting a portion of said operating charge into a steady-state helium arc ldischarge between said electrodes, said operating charge having an average steady-state operating pressure during said steady-state helium are discharge, a sealing-reservoir volume bounded by said outer envelope inner surface and said inner envelope outer surface, a helium gas sealing-reservoir charge contained within said sealing-reservoir volume and of such magnitude that its average pressure during said steady-state helium arc discharge approximates said average steadystate operating pressure of said operating charge, and a nitrogen gas starting charge contained within said sealingreservoir volume for maintaining said helium arc discharge within said inner envelope.

3. A helium arc lamp comprising a vitreous sealed outer envelope surrounding a fuzed quartz sealed doubleended inner envelope, said envelopes having inner and outer surfaces and lead-in conductors sealed therethrough, electrodes positioned within said inner envelope and substantially at opposite ends thereof and supported thereat by said lead-in conductors, an operating charge of helium contained within said inner envelope, said lead-in conductors and said electrodes being adapted to have applied thereto an energizing potential for ionizing and converting a portion of said operating charge into a steady-state helium arc discharge between said electrodes, said operating charge having an average steady-state operating pressure during said steady-state helium arc discharge, a sealing-reservoir volume bounded by said outer envelope inner surface and said inner envelope outer surface, a helium sealing-reservoir ycharge contained within said sealing-reservoir volume and of such magnitude that its average pressure during said steady-state helium arc discharge approximates said average steady-state operating pressure of said operating charge, and an argon gas starting charge contained within said sealing-reservoir volume for maintaining said helium arc discharge within said inner envelope. 4. A discharge lamp comprising a vitreous sealed outer envelope surrounding a fuzed quartz sealed double-ended inner envelope, said envelopes having inner and outer surfaces and lead-in conductors sealed therethrough, electrodes positioned within said inner envelope and substantiallyy at opposite ends thereof and supported thereat by said lead-in conductors, an operating charge of hydrogen gas contained within said inner envelope, said leadin conductors and said electrodes being adapted to have applied thereto an energizing potential for ionizing and converting a portion of said operating charge into a steadystate hydrogen arc discharge between said electrodes, said operating charge having an average steady-state operating pressure during said steady-state hydrogen arc discharge, a sealing-reservoir volume bounded by said outer envelope inner surface and said inner envelope outer surface, a hydrogen gas sealing-reservoir charge contained Within said sealing-reservoir volume and of such magnitude that its average pressure during said steady-state hydrogen arc discharge approximates said average steady-state operating pressure of said operating charge, and a starting charge contained within said sealing-reservoir volume for maintaining said hydrogen arc discharge within said inner envelope.

5. A spectroscopic lamp comprising a helium gas irnpervious, vitreous sealed outer envelope surrounding a fuzed quartz sealed double-ended inner envelope, said envelopes having inner and outer surfaces and lead-in conductors sealed therethrough, electrodes positioned within said inner` envelope and substantially at opposite ends thereof and supported thereat by said lead-in conductors, an operating charge of helium gas contained within said inner envelope, said lead-in conductors and said electrodes being adapted to have applied thereto an energizing potential for ionizing and convertingl a portion of said operating charge into a steady-state helium arc discharge between said electrodes, said operating chargek having an average steady-state operating pressure during said steady-state helium arc discharge, a sealing-reservoir volume bounded by said outer envelope inner surface and said inner envelope outer surface, a helium gas sealingreservoir charge contained within said sealing-reservoir volume and of such magnitude that its average pressure during said steady-state helium are discharge approximates said average steady-state operating pressure of said operating charge, a starting charge of nitrogen gas contained within said sealing-reservoir volume, and said starting charge and said sealing-reservoir charge having nonoperating pressures totalling approximately one atmosphere.

6. A hydrogen discharge lamp comprising a vitreous sealed outer envelope surrounding a fuzed quartz sealed double-ended inner envelope, said envelopes having inner and outer surfaces and lead-in conductors sealed therethrough, electrodes positioned within said inner envelope and substantially at opposite ends thereof and supported thereat by said lead-in conductors, an operating charge of hydrogen contained within said inner envelope, said lead-in conductors and said electrodes being adapted to have applied thereto an energizing potential for ionizing andfconverting a portion of said operating charge into a steady-state hydrogen arc discharge between said electrodes, said operating charge having an average steadystate operating pressure during said steady-state hydrogen arc discharge, a sealing-reservoir volume bounded by said outer envelope inner surface and said inner envelope outer surface, a hydrogen sealing-reservoir charge vcontained within said sealing-reservoir volume and of such magnitude that its average pressure during said steady-state hydrogen arc discharge approximates said average steady-state operating pressure of said operating charge, the average pressure of said hydrogen operating charge during said steady-state arc discharge being from 0.6 to 0.8 mm. mercury and a starting charge contained within said sealing-reservoir volume for maintaining said hydrogen arc discharge within said inner envelope.

7. A hydrogen discharge lamp comprising a vitreous sealed outer envelope surrounding a fuzed quartz sealed double-ended inner envelope, said envelopes having inner and outer surfaces and lead-in conductors sealed therethrough, electrodes positioned Within said inner envelope and substantially at opposite ends thereof and supported thereat by said lead-in conductors, an operating charge of hydrogen contained within said inner envelope, said lead-in conductors and said electrodes being adapted to have applied thereto an energizing potential for ionizing and converting a portion of said operating charge into a steady-state hydrogen arc discharge between said electrodes, said operating charge having an average steadystate operating pressure during said steady-state hydrogen arc discharge, a sealing-reservoir volume bounded by said outer envelope inner surface and said inner envelope outer surface, a hydrogen sealing-reservoir charge contained within said sealing-reservoir volume and of such magnitude that its average pressure during said steadystate hydrogen arc discharge approximates said average steady-state operating pressure of said operating charge, the average pressure of said hydrogen operating charge during said steady-state arc discharge being from 0.6 to 4 mm. mercury, and a starting charge contained within said sealing-reservoir volume for maintaining said hydrogen arc discharge within said inner envelope.

8. A helium discharge lamp comprising a vitreous sealed outer envelope surrounding a fuzed quartz sealed double-ended inner envelope, said envelopes having inner and outer surfaces and lead-in conductors sealed therethrough, electrodes positioned within said inner envelope and substantially at opposite ends thereof and supported thereat by said lead-in conductors, an operating charge of helium contained Within said inner envelope, said lead-in conductors and said electrodes being adapted to have applied thereto an energizing potential for ionizing and converting a portion of said operating charge into a steady-state helium arc discharge between said electrodes, said operating charge having an average steady-state operating pressure during said steady-state helium are discharge, a sealing-reservoir volume bounded by said outer envelope inner surface and said inner envelope outer surface, a helium sealing-reservoir charge contained within said sealing-reservoir volume and of such magnitude that its average pressure during said steady-state helium arc discharge approximates said average steady-state operating pressure of said operating charge, the average pressure of said helium operating charge during said steadystate arc discharge being from 0.5 to 1.0 mm. mercury, and a starting charge contained within said sealingreservoir volume for maintaining said helium arc discharge Within said inner envelope.

9. A helium discharge lamp comprising a vitreous sealed outer envelope surrounding a fuzed quartz sealed double-ended inner envelope, said envelopes having inner and outer surfaces and lead-in conductors sealed therethrough, electrodes positioned within said inner envelope and substantially at opposite ends thereof and supported thereat by said lead-in conductors, an operating charge of helium contained within said inner envelope, said leadin conductors and said electrodes being adapted to have applied thereto an energizing potential for ionizing and converting a portion of said operating charge into a steady-state helium arc discharge between said electrodes, said operating charge having an average steady-state operating pressure during said steady-state helium arc discharge, a sealing-reservoir volume bounded by said outer envelope inner surface and said inner envelope outer surface, a helium sealing-reservoir charge contained Within said sealing-reservoir volume and of suchv magnitude that its average pressure during said steady-state helium are discharge approximates said average steady-state operating pressure of said operating charge, the average pressure of said helium operating charge during said steady-state arc discharge being from 0.5 mm. to 6.0 mm. mercury, and a starting charge contained Within said sealing-reservoir volume for maintaining said helium are discharge within said inner envelope.

References Cited in the tile of this patent UNITED STATES PATENTS 2,315,286 Hayes Ir. et al. Mar. 30, 1943 2,392,305 Beese Jan. 8, 1946 2,545,884 Isaacs et al. Mar. 20, 1951 2,562,887 Beese Aug. 7, 1951 FOREIGN PATENTS 473,332 Great Britain Oct. 6, 1937 

1. A LIGHT GAS DISCHARGE LAMP COMPRISING A VITREOUS SEALED OUTER ENVELOPE SURROUNDING A FUZED QUARTZ SEALED DOUBLE-ENDED INNER ENVELOPE, SAID ENVELOPES HAVING INNER AND OUTER SURFACES AND LEAD-IN CONDUCTORS SEALED THERETHROUGH, ELECTRODES POSITIONED WITHIN SAID INNER ENVELOPE AND SUBSTANTIALLY AT OPPOSITE ENDS THEREOF AND SUPPORTED THEREAT BY SAID LEAD-IN CONDUCTORS, AN OPERATING CHARGE OF LIGHT GAS CONTAINED WITHIN SAID INNER ENVELOPE, SAID LEAD-IN CONDUCTORS AND SAID ELECTRODES BEING ADAPTED TO HAVE APPLIED THERETO AN ENERGIZING POTENTIAL FOR INONIZING AND CONVERTING A PORTION OF SAID OPERATING CHARGE INTO A STEADY-STATE LIGHT GAS ARC DISCHARGE BETWEEN SAID ELECTRODES, SAID OPERATING CHARGE HAVING AN AVERAGE STEADYSTATE OPERATING PRESSURE DURING SAID STEADY-STATE LIGHT GAS ARC DISCHARGE, A SEALING-RESERVOIR VOLUME BOUNDED BY SAID OUTER ENVELOPE INNER SURFACE AND SAID INNER ENVELOPE OUTER SURFACE, A LIGHT GAS SEALING-RESERVOIR CHARGE CONTAINED WITHIN SAID SEALING-RESERVOIR VOLUME AND OF SUCH MAGNITUDE THAT ITS AVERAGE PRESSURE DURING SAID STEADYSTATE LIGHT GAS ARC DISCHARGE APPROXIMATES SAID AVERAGE STEADY-STATE OPERATING PRESSURE OF SAID OPERATING CHARGE, AND A STARTING CHARGE CONTAINED WITHIN SAID SEALING-RESERVOIR VOLUME FOR MAINTAINING SAID LIGHT GAS ARC DISCHARGE WITHIN SAID INNER ENVELOPE. 